This was asked about in Question 9 from the second paper of 2009. Question 23 from the first paper of 2010 and the near-identical Question 6 from the second paper of 2016 ask specifically about procalcitonin, because it is the hot new thing.

One can find a plethora of articles on this topic, all unimaginatively titled "Biomarkers of sepsis":

CRP: cheap, easy, but also elevated in non-infective situations eg. MI, burns, surgery, trauma, autoimmune disease - and not as specific as procalcitonin

Procalcitonin: quick, more specific for bacterial sepsis than CRP, but expensive. For the discrimination of infectious from non-infectious cause of fever, the clinical judgement of an ED physician is at least equally accurate, if not better.

To make more detail available, the markers, their properties, advantages and disadvantages have been compiled into the table below. Where possible, references to the relevant publication are included. Elsewhere the main reference is Cho and Choi's review paper. If the time-poor exam candidate were to limit themselves to only one article, they could do much worse. Again, Oh's Manual is useless for this purpose; two paragraphs are devoted to biomarkers of sepsis on page 720 of the 7th edition (in Chapter 69 by De Gaudio).

Procalcitonin in detail

The college loves procalcitonin. It has been the subject of Question 23 from the first paper of 2010 and the near-identical Question 6 from the second paper of 2016. The cancidates were asked to critically evaluate the use of procalcitonin, quoting some studies where possible. The answer to these questions is reproduced below to simplify revision:

Introduction / definition:

Procalcitonin is the prohormone of calcitonin, normally synthesised by the C-cells of the thyroid gland, but produced ectopically by lung and intestine in the context of sepsis. As such, it is an attractive biomarker, and has been the subject of interesting research.

Rationale:

Procalcitonin may be useful in identifying occult infection; levels peak within 6-8 hours after the first appearance of endotoxin, and this it may identify patients with severe infection before blood cultures have time to incubate, and before more serious manifestations of sepsis have time to evolve.